Submission #1248068

#	Time	Username	Problem	Language	Result	Execution time	Memory
1248068		dzhoz0	One-Way Streets (CEOI17_oneway)	C++20	0 / 100	3 ms	4928 KiB

oneway

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define INF 1e18
#define f first
#define s second
#define pii pair<int, int>
#define vi vector<int>

const int MOD = 1'000'000'000 + 7;

void setIO(string name = "")
{
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
#ifdef LOCAL
    freopen("inp.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
#else
    if (!name.empty())
    {
        freopen((name + ".INP").c_str(), "r", stdin);
        freopen((name + ".OUT").c_str(), "w", stdout);
    }
#endif
}


// START OF DEBUG
#define db(val) "["#val" = "<<(val)<<"] "
#define print_op(...) ostream& operator<<(ostream& out, const __VA_ARGS__& u)
// for printing std::pair
template<class U, class V> print_op(pair<U, V>) {
    return out << "(" << u.first << ", " << u.second << ")";
}
// for printing collection
template<class Con, class = decltype(begin(declval<Con>()))>
typename enable_if<!is_same<Con, string>::value, ostream&>::type
operator<<(ostream& out, const Con& con) { 
    out << "{";
    for (auto beg = con.begin(), it = beg; it != con.end(); ++it)
        out << (it == beg ? "" : ", ") << *it;
    return out << "}";
}
// for printing std::tuple
template<size_t i, class T> ostream& print_tuple_utils(ostream& out, const T& tup) {
    if constexpr(i == tuple_size<T>::value) return out << ")"; 
    else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); 
}
template<class ...U> print_op(tuple<U...>) {
    return print_tuple_utils<0, tuple<U...>>(out, u);
}
// END OF DEBUG

const int MAXN = 1e5;
int n, m;
vector<pii> g[MAXN + 5];
vector<pii> tree[MAXN + 5];

int low[MAXN + 5];
int num[MAXN + 5];
int id[MAXN + 5];
vi nodes;
int sccCount = 0;
int timerDfs = 0;
void dfs(int u, int par) {
    low[u] = num[u] = ++timerDfs;
    nodes.push_back(u);
    bool skip = false; 
    for(auto [v, id] : g[u]) {
        if(v == par && !skip) {
            skip = true;
            continue;
        }
        if(num[v] == 0) {
            dfs(v, u);
            low[u] = min(low[u], low[v]);
        }
        else {
            low[u] = min(low[u], num[v]);
        }
    }

    if(low[u] == num[u]) {
        sccCount++;
        int v;
        do {
            v = nodes.back();
            id[v] = sccCount;
            nodes.pop_back();
        }
        while(v != u);
    }
}



int val[MAXN + 5];
int ans[MAXN + 5];
// ans[i] : (-1, L) ; (0 : B) ; (1; R)
void dfs_ans(int u, int par) {
    for(auto [v, index] : tree[u]) {
        if(v == par) continue;
        dfs_ans(v, u);
        if(val[v] > 0) {
            if(index > 0) ans[index] = -1;
            else ans[-index] = 1;
        }
        else if (val[v] < 0){
            if(index > 0) ans[index] = 1;
            else ans[-index] = -1;
        }
        val[u] += val[v];
    }
}

void solve()
{
    cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int u, v; cin >> u >> v; 
        if(u == v) continue;
        g[u].push_back({v, i});
        g[v].push_back({u, -i});
    }

    for(int i = 1; i <= n; i++) if(num[i] == 0) dfs(i, -1);


    for(int u = 1; u <= n; u++) {
        for(auto [v, i] : g[u]) {
            if(id[u] != id[v]) {
                tree[id[u]].push_back({id[v], i});
            }
        }
    }


    int q; cin >> q;
    while(q--) {
        int u, v; cin >> u >> v;
        u = id[u];
        v = id[v];
        val[u]++;
        val[v]--;
    }

    dfs_ans(id[1], id[1]);
    
    // for(int i = 1; i <= sccCount; i++) cout << i << ' ' << ans[i] << '\n';

    for(int i = 1; i <= m; i++) {
        if(ans[i] == 0) cout << 'B';
        else if(ans[i] == -1) cout << 'L';
        else if(ans[i] == 1) cout << 'R';
    }
}
signed main()
{
    setIO();
    int t = 1;
    // cin >> t;
    while (t--)
        solve();
}

Compilation message (stderr)

oneway.cpp: In function 'void setIO(std::string)':
oneway.cpp:23:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   23 |         freopen((name + ".INP").c_str(), "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
oneway.cpp:24:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   24 |         freopen((name + ".OUT").c_str(), "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 30
• Subtask 2: 0 / 30
• Subtask 3: 0 / 40